The spectrally resolved CT imaging (CT imaging) of a patient enables the creation of quantitative CT image data (CT image data). Spectrally resolved CT imaging is possible, for example, by way of known dual-energy processes or with the use of energy-sensitive detectors. The quantitative CT image data can comprise information relating to a spatially resolved distribution of a material coefficient, for example, an electron density and/or a mass density and/or an effective atomic number distribution and/or a stopping power and/or a linear attenuation coefficient at a particular photon energy or for a particular photon energy spectrum, in a body of the patient. In place of a patient, the quantitative CT image data can also be acquired from any desired examination object, for example, an article or a test subject.
Particularly advantageously, dual-source CT devices are suitable for spectrally resolved CT imaging, since these can simultaneously acquire the CT scan data (CT scan data) for different energy spectra. From U.S. Pat. No. 8,588,363 B2, there is known an example dual-source CT device. From U.S. Pat. No. 8,897,530 B2, there is known a dual-source CT device by which a proportion of necrotic tissue can be determined.
In particular, where dual-source CT devices (dual-source CT devices) are used which comprise a first radiation source-detector system and a second radiator source-detector system wherein the first radiation source-detector system is operated with a different energy spectrum from that of the second radiation source-detector system, a scanning region in which spectrally resolved information is present can be smaller than a maximum possible scanning field of the dual-source CT device. A reason for this can be, in particular, that the first radiation source-detector system has a larger fan-beam arc and thus a greater capture region than the second radiation source-detector system. The spectrally resolved information then lies, in particular, only in the circular subregion of the scanning field of the dual-source CT device which, on rotation of both radiation source-detector systems is jointly covered. The first radiation source-detector system with the larger fan-beam arc can, however, typically cover the whole scanning field of the dual-source CT device, wherein the whole scanning field is larger than the subregion of the scanning field in which the spectrally resolved information is present. In the outer subregion of the scanning field which is then additionally present, with conventional reconstruction methods there is initially no spectrally resolved information, so that a calculation of the quantitative CT image data in this outer subregion is not possible with conventional spectral methods.